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outdoor coil frosting

while performing heat check upon arriving at heat pump the coil was frosted in sections and the distributor lines were frosted upto liquid line port. pressure was lower that normal. again check is in heat mode. charged unit with 2 lbs of 410a. pressures were up but still had some frosting on liquid line. did i not charge enough or could there be other issues such as a restriction in txv or drier?

Mine was frosting quickly this AM as was mid 30s F and 99% humidity (PNW) - them there BTUs gotta come from someplace, if you look at a psychrometric chart for humidity and temp frost may be what should be expected.

Here in PNW on HPs with a timer on the defrost the entire outdoor coil is often solid frost 1/2" thick before defrost kicks in.

Your 'frosting on liquid line' could indicate a stuck reversing valve? Never have seen a liquid line with frost in this climate.

with the information provided cant really help ya. Could be installer did not install correctly... Did you check filter or coil (AHU) to see if they were dirty.... Possible txv issue but I doubt it or it would have been iced up badly or completely shut down on you. More info needed when you need help like that or like dgussler says....Build yourself a fire..... Wont get too much help unless you provide info....

If it's running in heat mode and it's somewhat cold outside. That is generally what a heat pump does when it runs. It's starts icing up the outdoor coil. That is why it has a defrost mode. To melt the ice that accumulates on it while it is running. Now if you have 3 inches of ice on the coil and the fan can't turn anymore because there's so much ice, then you probably have a problem.